title: The CO2-concentrating mechanism of Synechococcus WH5701 is composed of native and horizontally-acquired components.
abstract: The cyanobacterial CO(2)-concentrating mechanism (CCM) is an effective adaptation that increases the carbon dioxide (CO(2)) concentration around the primary photosynthetic enzyme Ribulose-1,5-bisphosphate Carboxylase/Oxygenase (RuBisCO). α-Cyanobacteria (those containing Form1-A RuBisCO within cso-type α-carboxysomes) have a limited CCM composed of a small number of Ci-transporters whereas β-cyanobacteria (those species containing Form-1B RuBisCO within ccm-type β-carboxysomes) exhibit a more diverse CCM with a greater variety in Ci-transporter complement and regulation. In the coastal species Synechococcus sp. WH5701 (α-cyanobacteria), the minimal α-cyanobacterial CCM has been supplemented with β-cyanobacterial Ci transporters through the process of horizontal gene transfer (HGT). These transporters are transcriptionally regulated in response to external Ci-depletion however this change in transcript abundance is not correlated with a physiological induction. WH5701 exhibits identical physiological responses grown at 4% CO(2) (K (1/2) ≈ 31 μM Ci) and after induction with 0.04% CO(2) (K (1/2) ≈ 29 μM Ci). Insensitivity to external Ci concentration is an unusual characteristic of the WH5701 CCM which is a result of evolution by HGT. Our bioinformatic and physiological data support the hypothesis that WH5701 represents a clade of α-cyanobacterial species in transition from the marine/oligotrophic environment to a coastal/freshwater environment.
authors.affiliation: Division of Plant Science, Research School of Biology, College of Medicine, Biology and Environment, The Australian National University, Canberra, ACT, Australia.
authors.forename: Benjamin D
authors.initials: BD
authors.lastname: Rae
authors.forename: Britta
authors.initials: B
authors.lastname: Förster
authors.forename: Murray R
authors.initials: MR
authors.lastname: Badger
authors.forename: G Dean
authors.initials: GD
authors.lastname: Price
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics* / Q000378:metabolism; D005075:Biological Evolution; D001692:Biological Transport; D002244:Carbon / Q000378:metabolism*; D002245:Carbon Dioxide / Q000378:metabolism* / Q000494:pharmacology; D019295:Computational Biology; D000458:Cyanobacteria / Q000145:classification / Q000235:genetics; D005618:Fresh Water / Q000382:microbiology; D015964:Gene Expression Regulation, Bacterial; D022761:Gene Transfer, Horizontal / Q000235:genetics*; D044404:Genomic Islands; D010788:Photosynthesis; D010802:Phylogeny; D012329:RNA, Bacterial / Q000235:genetics; D012273:Ribulose-Bisphosphate Carboxylase / Q000235:genetics / Q000378:metabolism; D012274:Ribulosephosphates / Q000378:metabolism; D012623:Seawater / Q000382:microbiology; D016415:Sequence Alignment; D046940:Synechococcus / Q000145:classification / Q000235:genetics / Q000378:metabolism / Q000502:physiology*
chemical_list: D001426:Bacterial Proteins; D012329:RNA, Bacterial; D012274:Ribulosephosphates; D002245:Carbon Dioxide; C001933:ribulose-1,5 diphosphate; D002244:Carbon; D012273:Ribulose-Bisphosphate Carboxylase